The invention relates to an apparatus for winding a tape-like material from a supply reel onto a take-up reel, in which tape-guide elements guide the tape-like material along a given tape-guide path and in which at least one winding device drives the reels.
In magnetic-tape video apparatuses fast forward or reverse winding of the magnetic tape is possible for the purpose of replaying or fast-motion reproduction. The magnetic tape can then be wound from a supply reel onto a take-up reel at up to 50 times its transport speed for normal reproduction. On its way to the take-up reel the magnetic tape travels in the customary manner past a rotating scanning device, a plurality of tape-guide elements and one or two tape-tension controllers. These tape-tension controllers control the torque of reel drives which drive the two reels to maintain a predetermined tape tension, and thereby determine the winding density of the magnetic tape wound onto the take-up reel. At a normal reproduction speed, for which the tape transport speed corresponds to the transport speed during recording, and at low winding speeds the magnetic tape can be wound with a satisfactory winding density. However, this is no longer the case at high winding speeds as a result of air which is trapped between the winding layers and which can escape only later. The attendant slackening of the tape then gives rise to a slacker winding, which leads to slipping of the winding layers, as a result of which the tape tension and the tape transport speed may vary abruptly, so that tape loops are formed in the transport path of the magnetic tape.
A method of avoiding tape loops during winding of magnetic tape is known from JP 61-104352. In this known method the driver stages of the winding motors for the magnetic tape receive a phase-shifted pulse signal which influences the current through the winding motors in such a manner that the tape tension of the magnetic tape varies with a period of 100 ms.
Moreover, U.S. Pat. No. 3,019,999 describes a winding device in which a web material is unwound from a supply reel at a given speed of transport and is wound onto a drive shaft whose torque is interrupted periodically.
Finally, DE-41 30 791 A1 discloses a device for winding string-shaped or web-shaped materials onto a take-up roller which is driven by a drive means, in which the drive means alternately exerts a comparatively low tractive force on the material in a first time interval and a comparatively high tractive force in a second time interval in order to tauten the material taken up in the first time interval.
The known devices have the disadvantage that for a dense winding pulsating torques are applied to the magnetic tape via the reel drive of the take-up reel. However, the magnitude of the applied pulsating torques is not constant but varies with the instantaneous winding diameter and the moment of inertia of the winding. A satisfactory winding density can be obtained only for a small take-up diameter because the tape tension is then higher than in the case of large take-up diameters. However, a higher tape tension reduces the life of the rotating magnetic heads of the scanning device.